The present invention relates generally to in vehicle navigation or route guidance systems, and more particularly to an improved display for such a system.
Navigation systems include a graphical user interface having a display which displays the current position of a vehicle on a map. The display of the roads on the map in particular may include curved or diagonal lines which may appear jagged, due to the limited resolution of the display. Although increasing the resolution of the display would alleviate this problem, this would also increase the cost of the display and the power required for the processor handling the display.
It is known to use anti-aliasing on home computer displays to reduce the jagged appearance of lines which are not perfectly vertical or horizontal, i.e. perfectly aligned with the columns or rows on the display. In the known anti-aliasing technique for computer displays each pixel includes a red, green and blue numerical value which preciously defines the color of that pixel. A displayed line formed as a plurality of discrete pixels is compared mathematically to the ideal desired line. Pixels which are not completely on the ideal line are evaluated mathematically relative to the ideal. For example, one pixel on a line may be half inside and half outside the ideal line. Half of that pixel would ideally be the color of the line or object and the other half of that pixel would ideally be the color of the background. The color of that pixel is altered to a color which is a weighted average of the color of the line and the color of the background. The weighting of the color is proportional to the amount that the pixel is inside versus outside the ideal. For example, if the pixel were 80 percent in the ideal line, the red, green and blue values for that pixel would each be 80 percent of the values for the line plus 20 percent of the values for the background color.
In order to reduce computation time and power, the navigation system may use paletted colors, in which there are only a limited number of colors available at any one time. Each of the palette's colors can be any color. Each pixel in the display includes an index to the color palette indicating the color that the pixel is to be displayed. The color that is the weighted average of the line or object in background is probably not available. As a result, the bordering pixels in a line or object on a navigation system display cannot be anti-aliased according to the known technique.